The present invention relates to a process for producing mono, bis or tris(3,3,3-trifluoropropyl)benzene.
In prior arts, it is unknown reaction system that mono-, bis- or tris(3,3,3-trifluoropropyl)benzene is producing from 3,3,3-trifluoropropylene and benzene by Friedel-Crafts type reaction. As a process for producing 3,3,3-trifluoropropylbenzene, a certain process has been proposed in U.S. Pat. No. 3,080,428, in which process 3,3,3-trifluoropropyl ether is brought into reaction with benzene in the presence of hydrogen fluoride. However, since in the proposed process, water is formed from the reactants, the catalytic activity is reduced during the reaction and the recovery of once used catalyst is difficult. In addition, since the starting material, 3,3,3-trifluoropropyl ether, is obtained by the reaction of expensive vinylidene fluoride, formaldehyde or its polymer and hydrogen fluoride in a yield as low as 50 to 60%, the thus obtained 3,3,3-trifluoropropyl ether is highly expensive.
Whereas in the process of the present invention, since the product of the present invention is synthesized by the reaction of an industrial starting material, 3,3,3 -trifluoropropylene and benzene in the presence of an acid catalyst, not only the process needs only one reaction step but also the catalytic activity is maintained during and after the reaction is over because no water is formed by the above-mentioned reaction, and the recovery of the once used catalyst is extremely easy.
It is an object of the present invention to provide a process for producing 3,3,3-trifluoropropylated benzene derivative represented by the following formula ##STR1## wherein n is an integer of 1, 2 or 3, which comprises bringing benzene into reaction with 3,3,3-trifluoropropylene in the presence of an acid catalyst selected from the group consisting of hydrogen fluoride, boron trifluoride and a mixture thereof. A further object is to provide bis(3,3,3-trifluoropropyl)benzene, and bis(3,3,3-trifluoropropyl)benzene obtained by the process thereabove. Other objects and advantages of the present invention will be apparent hereinafter.
Mono, bis or tris(3,3,3-trifluoropropyl)benzene is useful for a variety of purposes, for instance, in the organic synthesis of pharmaceuticals or agricultural chemicals as an intermediate compound.
Since 3,3,3-trifluoropropylene used in the process of the present invention has an electron-withdrawing group, trifluoromethyl, the basicity of the carbon-carbon double bond of the above-mentioned molecule of trifluoropropylene is far weaker than that of propylene having an electron-releasing group, methyl, a presence of a strongly acidic Friedel-Crafts' catalyst, is necessary in the reaction. However, in the case where aluminum chloride, i.e., a representative Friedel-Crafts' catalyst, is used, side reactions such as substitution by chlorine atom or cyclization of the reactants take place. For instance, in the reaction of benzene and 3,3,3-trifluoropropylene in the presence of aluminum chloride, the yield of 3,3,3-trifluoropropylbenzene is only a little with the by-production of (3-chloro-3,3-difluoropropyl)benzene; (3,3-dichloro-3-fluoropropyl)benzene; (3,3,3-trichloropropyl)benzene; 1,1-difluoroindan; 1-chloro-1-fluoroindan; 1,1-dichloroindan; etc.
On the other hand, ferric chloride which is weaker than aluminum chloride is almost ineffective in the present reaction. In addition, in the case where silica-alumina is used as the catalyst, the yield of the aimed compound is extremely poor due to the various side reactions.
As a result of keen efforts of the inventors of the present invention to find out a suitable catalyst for the purpose of the present reaction, hydrogen fluoride, boron trifluoride and a mixture thereof have been found to be the effective catalyst, and the present invention has been attained.
Since the catalyst used in the present process is a gaseous substance or a low-boiling liquid, the once used catalyst can be removed from the reaction system easily by stripping and the recovery and re-use of the once used catalyst are possibly carried out easily. In carrying out the process of the present invention, the catalyst is preferably used in an amount of more than 0.5 mole per mole of benzene.
The temperature of the reaction depends upon the species of catalyst. From the viewpoint of the catalytic activity, the temperature at which the catalyst shows its activity is highest in the case of hydrogen fluoride, followed by boron trifluoride and then by a mixture thereof. For instance, in the case of hydrogen fluoride, the reaction is preferably carried out at a temperature of 50.degree. to 150.degree. C.; in the case of boron trifluoride, the reaction is preferably carried out at a temperature of 0.degree. to 120.degree. C.; and, in that of a mixture of hydrogen fluoride and boron trifluoride, the reaction is preferably carried out at -20.degree. to 100.degree. C.
The reaction of the present process is shown by the following reaction formula: ##STR2## wherein n is an integer of 1, 2 or 3.
Namely, the reaction of the present process is quite different from the addition of propylene to aromatic compound, which gives isopropyl-substituted aromatic compound, and the presence of 3,3,3-trifluoropropyl group in the reaction product of the present process has been confirmed by the nuclear magnetic resonance spectra of .sup.1 H and of .sup.19 F, respectively of the product of the present invention.
After the reaction of the present process is over, the residual gas is purged from the reaction system by stripping and the residue is neutralized, washed with water or filtered following the conventional steps, and the product is collected by distillation under a reduced pressure.
The preferable reaction condition for obtaining mainly mono- or bis(3,3,3-trifluoropropyl)benzene is shown in Table 1.
TABLE 1 ______________________________________ Summary of preferable reaction condition Reaction condition Molar amount of 3,3,3-trifluoro- ropropylene per Product mole of benzene ______________________________________ Mono(3,3,3-trifluoropropyl)- benzene ##STR3## 0.5 .about. 1.5 Bis(3,3,3-trifluoropropyl)- benzene ##STR4## 1.5 .about. 2.5 ______________________________________